A conventional electronic component of this type will be described with reference to FIGS. 4A and 4B. FIG. 4A is a perspective view of a circuit protective element which is an example of the conventional electronic component. FIG. 4B is a sectional view of the circuit protective element, seen along an A-A line in FIG. 4A.
As shown in FIGS. 4A and 4B, the circuit protective element is configured by: a base 1; a conductive film 2; a protective film 5; and a plating layer 7. The base 1 is shaped like a pillar, such as a column and a prism. It is made of any of ceramic, glass, and a mixture of ceramic and glass, which have an insulation characteristic. The conductive film 2 is made of copper, silver, nickel or the like. It is formed over the entire surface of the base 1. An electrode 6 is formed by each of the portions of the conductive film 2 which are located at both end portions of the base 1. A plating layer 7 is formed on the surface of the electrode 6. The protective film 5 is made of epoxy resin or the like. It is formed so as to cover the portion of the conductive film 2's surface except its portions located at both end portions of the base 1.
A portion of the conductive film 2 is cut off by means of laser irradiation or the like. Thereby, a resistance-adjusting groove 3 is created in the conductive film 2. It makes substantially one turn so that its tips overlap each other. The region between the portions in which the tip portions of the resistance-adjusting groove 3 overlap each other is a narrow portion 4. As an electronic component which has such a groove, for example, there is a chip component which is disclosed in Japanese Patent Laid-Open No. 7-307201 specification.
Herein, the conductive film 2 is a portion which fulfills the electrical function of the circuit protective element. For example, if an electronic component is a resistor, it becomes a resistant body. In the case of the circuit protective element shown in FIGS. 4A and 4B, it turns into a fusing portion with a fusing function. In this case, if an over-current beyond a certain level is applied, the narrow portion 4 provided in the conductive film 2 generates heat. Thereby, it is melted and fused. This breaks the current which is applied on the circuit protective element.
Next, a manufacturing method will be described for the above described circuit protective element. First, over the whole surface of the base 1, the conductive film 2 is formed by means of plating. In this case, the electrode 6 is formed by the conductive film 2 located at both end portions of the base 1.
Sequentially, the conductive film 2 is irradiated with a laser beam to cut off a portion of the conductive film 2. Thereby, the resistance-adjusting groove 3 is formed which has substantially one turn so that its tips overlap each other. At this time, the narrow portion 4 is formed within the region between the overlapped portions in the tip portions of the resistance-adjusting groove 3.
Next, the protective film 5 made of epoxy resin or the like is formed to cover the surface of the conductive film 2 other than the portions located at both end portions of the base 1. Finally, the plating layer 7 is formed on the surface of the electrode 6.
In the circuit protective element which is manufactured in this way, a resistance value is measured in its manufacturing process, or the resistance-adjusting groove 3 is formed. In order to take such a measurement, the circuit protective element needs to be held. A chuck is pressed against the electrode 6 so as to come into contact with it. Thereby, the circuit protective element can be held.
At this time, if the contact resistance between the chuck and the electrode 6 becomes greater, the contact resistance at this portion may adversely affect the measurement of a resistance value. This makes it impossible to adjust the resistance value precisely. Therefore, the contact resistance between the chuck and the electrode 6 has to be made as low as possible. In order to reduce the contact resistance between the chuck and the electrode 6, the chuck needs to be pressed on the electrode 6 by a strong force.
On the other hand, in the above described circuit protective element, the conductive film 2 is formed on the entire surface of the base 1. Thereby, the conductive film 2 is united with the electrode 6 which is located at both end portions of the base 1. In this case, the conductive film 2 and the electrode 6 are continuously formed, thus helping stabilize their electrical and mechanical connection.
However, if the conductive film 2 and the electrode 6 are continuously united, then depending upon the circuit protective element's resistance value, the conductive film 2 becomes thinner and the electrode 6 also thins down. At this time, in order to lower the contact resistance between the chuck and the electrode 6, the chuck is pressed against the electrode 6 by a strong force. Then, the base 1 cannot absorb all the mechanical impact at the time when it is pressed, and thus, the corner portions at both end portions of the base 1 may be chipped. This is because the base 1 is made of any of ceramic, glass, and a mixture of ceramic and glass. If the circuit protective element which has such a chip in its corner portions is mounted on a printed board or the like, its stable electrical connection cannot be obtained. Hence, the circuit protective element with any chips in the corner portions has to be removed, thus deteriorating its yield when manufactured.